Discharge device



y 1962 G. w. HARVEY ET AL 3,

DISCHARGE DEVICE Filed March 23, 1959 Sates The present inventionrelates to a vapor-arc discharge device which employs a pool-typecathode, and more particularly such a discharge device which includes anovel electrode for initiating the formation of an are.

In previously available vapor-arc discharge devices of the type whichemploy mercury pool-type cathodes, commonly known as Ignitrons, theignitor electrode, which is utilized to initiate the arc in theignitron, has generally been disposed directly between the anode and thepooltype cathode. Ordinarily, the ignitor electrode, which is composedof suitable material, has been supported by a bridge-type structure sothat its tip dips below the surface of the mercury pool. Because of thepresence of the ignitor structure in the path of the are, there is rapiddeterioration of the ignitor structure during high current operation.Moreover, it has been found that when the ignitor structure is locatedbetween the mercury pool cathode and the anode, high potential gradientsare formed which adversely afiect the forward breakdown voltage.

An object of the present invention is the provision of a vapor-arcdischarge device having improved life and electrical characteristics.Another object of the invention is the provision of a vapor-arcdischarge device which is adapted to be utilized in extremely highcurrent and high voltage pulse applications. Still another object i theprovision of a vapor-arc discharge device which is provided with anignitor which is generally electrostatically shielded from the anode,and which is displaced from the arc path between the anode and cathode.

Further objects and advantages of the P esent invention will becomeapparent by reference to the following description and accompanyingdrawings.

In the drawings:

FIGURE 1 is a longitudinal sectional view of a vaporarc discharge deviceembodying various features of the present invention; and

FIGURE 2 is a transverse sectional view taken along line 2--2 of FIGURE1.

Generally, the vapor-arc discharge device shown in the drawingscomprises an elongated evacuated envelope having a mercury pool-typecathode 12 disposed in one end thereof and an anode 14 extending fromthe opposite end into the interior of the envelope, the anode 14 beingspaced above the cathode 12. The discharge device is also provided withan ignitor electrode 16 which is disposed laterally of the anode 14 withits tip dipping into the surf-ace of the mercury pool 12 at a pointspaced laterally of the anode 14. In this way the ignitor electrode 16is completely displaced from the arc path between the anode 14- and thecathode 12. More specifically, applicants have now discovered that aredamage to the ignitor electrode of a mercury pool-type arc dischargedevice is eliminated by displacing the ignitor electrode 16 from the arcpath between the anode 14 and cathode 12. Moreover, applicants havefound that the forward break down voltage in such a discharge device isimproved by electrostatically shielding the ignitor electrode 16 fromthe anode 14.

More specifically, the anode 14, pooltype cathode 12 and ignitorelectrode 16 of the discharge device are all disposed in a conventionalmanner within an evacuated envelope 10 which may be of any suitableshape and construction. In the illustrated embodiment, the envelope 10includes a tubular outer casing 22 which is preferably made of metalsuch as stainless or cold-rolled steel. The lower end of the outercasing 22 is closed by a plate 24, also of metal, having a downwardlyturned peripheral flange 26, the rim of which is sealed as by welding tothe outer casing 22. The mercury pool-type cathode 12 of the dischargedevice is situated in the lower portion of the envelope 10, and sincethe metallic outer casing 22 makes contact with the mercury pool,electrical connection thereto may be obtained by contacting the metalliccasing 22 with a metal strap (not shown) or the like.

Extending downwardly into the upper end of the outer casing is the anode14, which in the illustrated embodiment includes a lower arcuate portion28 composed of graphite or the like, attached to a vertically extendingrod-like stud 30 of conductive material. The anode 14 is supportedwithin and insulated from the outer casing 22 by an upper closure wall32, the upper closure wall including a cup-shaped metallic cap 34 havingan outwardly and downwardly extending rim, and having an aperture 38disposed in the center thereof. A reduced diameter upper portion 36 ofthe stud 30 extends through the aperture 38 and the shoulder 39 formedon the stud 30 is suitably sealed to the cap 34. A sleeve 40' isdisposed over the reduced portion, the upper end of the sleeve 40 beingthreaded so that electrical connection may be made to the anode 14.

The edge of the rim of the cap 34 is sealed to the top rim of aninsulating sleeve 42 of a material such as glass, Mycalex, etc., and, inturn, the lower rim of the insulating sleeve is sealed to an innerupturned flange 44 of a ring 46. The ring 46 also is provided withanouter upturned flange 48 which is sealed to the upper end of the outercasing 22.

To prevent deterioration of the ignitor 16 due to arcing, the ignitor 16is positioned within the envelope 10 so that it is displaced from thearc path between the cathode 12 and the anode 14. In the illustratedembodiment, the tip of ignitor electrode 16 dips into the surface of thepool-type cathode 12 laterally of the anode 14 and extends upwardly andoutwardly at an angle from its tip, The ignitor 16, which is partiallymade of a high resistance material such as silicon carbide, boroncarbide, etc., includes an elongated body 52 which is reduced indiameter intermediate its ends for passage through the wall of theenvelope 10. Electrical connection to the ignitor 16 may be made at itsupper end.

In order to prevent the ignitor 16 from adversely affecting theelectrostatic field existing between the anode 14 and the cathode 12when a voltage is applied therebetween, the ignitor 16 is substantiallyelectrostatically shielded from the anode 14. However, so that the areinitiated by the ignitor 16 is transferred to the anode without delay,the tip of the ignitor electrode 16 is not electrostatically shielded.In the illustrated embodiment, the ignitor 16 is insulatingly supportedwithin a metallic tubular member 58 which extends upwardlyv in coaxialrelationship with the ignitor from an aperture 60 in the side of thecasing 22, the aperture 60 being disposed partially above the surface ofthe cathode 12. The tip of the ignitor 16 is immersed in the cathode 12at a position approximately even with the aperture 60. As illustrated,the end of the tubular member 58 is closed by a closure Wall 62 whichincludes an upwardly extending tubular portion 64. The reduced diameterintermediate portion of the ignitor 16 is sealed to the tubular portion64 by a glass body 66, By the above described construction the metaltubular member 58 and the metal outer casing 22 act as an electrostaticshield between the ignitor 16 and the anode 14, thereby preventing theignitor 16 from affecting the electrostatic field between the anode 14and the cathode 12.

After the envelope is assembled, sulficient mercury is added to immersethe tip of the ignitor 16, and then the envelope is evacuated through atubular member 68 which extends through the lower plate 24. The lowerend of the tubular member 68 is sealed, as shown in FIG- URE 1, afterthe envelope 10 is evacuated. When it is desired to set the dischargedevice in operation, va high voltage source (not shown) i connectedbetween the anode 14 and the cathode 12, and a second source of voltage(not shown) is connected between the ignitor 16 and the cathode 12. Whena suitable positive voltage is applied to the ignitor 16, a cathode spotis generally formed in the mercury pool adjacent the location of the tipof the ignitor 16, and if a suitable positive voltage is applied to theanode 14, the discharge device will conduct a current.

a From the above it can be seen that a mercury pool vapor-arc dischargedevice is provided in which an electrostatically shielded ignitor islocated so that it is displaced from the arc path between the anode andthe cathode. Such a vapor-arc discharge device has an extended lifesince arcing between the anode and ignitor is eliminated. Moreover, theforward breakdown voltage in such a device is increased and tends toremain constant from discharge to discharge.

Various changes and modifications may be made in the above describeddischarge device without departing from the spirit and scope of thepresent invention, Various of the features of the invention are setforth in the following claims.

We claim:

. 1. A vapor-arc-discharge device comprising an elongated verticallydisposed tubular casing, said casing having closure walls at both ends,a mercury pool-type cathode disposed in the lower portion of saidcasing, an anode extending through the upper closure wall and spacedabove said cathode, said casing having an aperture disposed partiallyabove the surface of the mercury pool, a tubular member extendingupwardly and outwardly at ,4 an angle from the aperture and having aclosure cap at its upper end, an electrode extending through said capand having its inner end dipped into the surface of the mercury pool atsaid aperture, said casing and saidtubular members being composed ofmetal intermediate the upper portion of the electrode and the anode andbeing at the same potential as said cathode, the aperture extending adistance above the cathode surface such that the upper portion of theelectrode is electrostatically shielded from the anode and anelectrostatic field extends between the anode and said electrode at saidinner end when voltage is applied to said anode.

2. A vapor-arc discharge device which comprises an evacuated envelope, amercury pool type cathode disposed in the lower end portion of saidenvelope, an anode disposed in said envelope and spaced above saidcathode, an ignitor electrode mounted laterally of said anode so thatthe tip thereof is below the surface of said mercury pool type cathodeat a point spaced laterally from the normal arc path between said anodeand said cathode, and an electrostatic shield disposed between saidignitor electrode and said anode to minimize distortion of theelectrostatic field that exists between said anode and said cathodeduring operation of the discharge device, said electrostatic shieldbeing spaced from the surface of said pool type cathode at a distancesuch that an electrostatic field is established directly between saidanode and the tip of said ignitor electrode, whereby an arc initiatedbysaid ignitor electrode during operation of the discharge device istransferred directly to said anode without delay.

References Cited in the file of this patent UNITED STATES PATENTS1,901,612 Schenkel Mar. 14, 1933 2,254,722 Aoki Sept. 2, 1941 2,595,716Smith May 6, 1952 2,673,308 Herring Mar. 23, 1954

